Clearly communicate your boundaries and limits with your mother-in-law in a calm and respectful manner. 
 

Try to maintain open and honest communication with your mother-in-law. State your opinions clearly when necessary.
 

Your relationship with your spouse should be your priority. Talk to your partner about how you both can handle the toxic situations.
 

Try to understand where your mother-in-law is coming from and what might be driving her behaviour. 
 

If situation gets worse, limit the amount of time you spend with your mother-in-law.